Heart Rhythm Disorders (cont.)

Benjamin Wedro, MD, FACEP, FAAEM

Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

What is a heart rhythm disorder (arrhythmia)?

When the heart's electrical system malfunctions, the normal rhythm of the heart can be affected. Depending upon the abnormality, the heart may begin to beat too fast, too slow, irregularly, or not at all. Heart rhythm disorders are often referred to as cardiac arrhythmias (cardiac = heart; a = lack of) but this is technically incorrect, since in most cases there is a heart rhythm, but it is abnormal. Cardiac dysrhythmia (dys = abnormal or faulty + rhythm) might be a better term.

Dysrhythmias may occur because of problems directly associated with the electrical "wiring," the SA node, the AV node, or ventricular conducting system. The issue may also be due to influences on the conducting system from outside the heart. These can include electrolyte abnormalities in the bloodstream, abnormal hormone levels (for example thyroid function that is too high or too low), and medication or drug ingestions.

Any abnormality of the electrical cycle within the heart that generates an abnormal beat, whether it is too fast, too slow, skipped, or irregular is considered a dysrhythmia.

Dysrhythmias are usually classified as originating from above the AV node (supraventricular ) or below, from the ventricle. They are either fast, slow, or irregular and persistent or intermittent.

What causes heart rhythm disorders?

Heart rhythm disturbances may occur because of problems within the heart itself or be the result of abnormalities in the body's environment that can affect the heart's ability to conduct electricity.

Cardiac or heart muscle cells become irritated when they are depleted of oxygen. This can occur during a heart attack, in which the coronary arteries, the blood vessels that supply the heart with blood, are blocked. Lack of oxygen can occur when the lungs are unable to extract oxygen from the air. Significant anemia, or low red blood cell count, decreases the oxygen-carrying capacity of the blood and may prevent adequate oxygen delivery. Rapid heart rates may be due to "wiring" problems with the electrical pathways in the heart. This can cause "short circuits" making the heart speed up and beat 150 beats a minute or more. The abnormality can be due to a physical extra electrical pathway such as that seen in Wolff-Parkinson-White (WPW) syndrome, or it can be due to changes in the electrical physiology between a few cells, like in atrial flutter.

Rapid heart rates can also occur because of environmental issues that affect the heart. These can be intrinsic to the body, like anemia, abnormal electrolyte levels, or abnormal thyroid hormone levels. They may also be due to reactions to outside influences like caffeine, alcohol, over-the-counter cold remedies, or stimulants such as amphetamines. To the cardiac muscle cell, they all appear to be adrenaline-like substances that can cause cell irritation.

Slow dysrhythmias can also be problematic. If the heart beats too slowly, the body may not be able to maintain an adequate blood pressure and supply the body's organs with enough oxygen-rich blood to function.

Slow heart rates may be due to aging of the SA node and its inability to generate an electrical pacemaker signal. Often though, it is due to the side effects of medications used to control high blood pressure. Side effects of beta blocker and certain calcium channel blocker drugs include a slowing of the heart rate.

Body environment is also important with slow heart rhythm abnormalities. Hypothermia, or low body temperature, is a potential cause.